Watt's separate condenser model No 1, 1769.
© Science Museum / Science & Society Picture Library
James Watt (1736-1819) fundamentally improved steam engine design with his separate condenser, which he patented in 1769. Early Newcomen engines were inefficient as their working cycle entailed continual heating and cooling of the cylinder, which wasted fuel. The separate condenser meant the steam was condensed in a separate chamber, allowing the cylinder to be kept hot and greatly increasing fuel efficiency. The SI (international standard) unit of power, the watt (W), is named after him.